1. Field of the Invention
The present invention relates to a vibration damper structure for subframes installed in automobiles, and to a subframe structure using the same. More particularly, the invention is concerned with a subframe structure equipped with detecting assembly for providing a signal for use as a detection signal for control in systems for controlling the state of travel of automobiles, and to rubber mounts for use in the subframe structure.
2. Description of the Related Art
There has long been research into suppressing unstable vehicle body behavior, such as slipping, through providing mechanical supplementation to the steering by the driver in order to improve the stability of motion of automobiles. Specifically, antilock braking systems (ABS) for suppressing the locking of wheels when braking have been brought to market, and there has been research into automobile control systems, such as for vehicle stability control, for the overall control of the stability of motion of vehicles, and for traction control to suppress slippage of wheels during acceleration.
These types of vehicle wheel control are performed using a variety of detection signals corresponding to the state of motion of the vehicle. A variety of structure have been proposed for detecting external forces acting upon the wheels such as the road friction and the effective vertical force, and detecting, for example, the coefficient of friction with the road surface, as structure for detecting these signals. JP-B-2628444, JP-A-2001-191767 and JP-A-2002-316502 disclose examples of such structure.
However, in a structure that is provided with embedded deformation gauges, equipped in holes in the axles, as described in the aforementioned JP-B-2628444, such structure are difficult to commercialize when one considers the strength and structure of the axles and when one considers manufacturability. In practice, since it is necessary to provide a plurality of holes in the axles in order to detect forces in a plurality of directions, there is a problem in that commercialization is all the more difficult.
Moreover, in a structure that is arranged for sensing deformation, rotation, etc., of the tire from the outside through the provision of detector targets on the tire, such as described in the aforementioned JP-A-200 1-191767, there are problems in that there is the risk that the performance of the tire will be compromised by the installation of the detection targets added to the tire. In addition to the problem of the likelihood of damage to the detection targets from flying gravel, mud, etc., from the surface of the road, and while the speed of rotation of the wheel can be detected easily, there is a problem in that it is extremely difficult to calculate, from the detected values, the external forces acting on the wheels.
Furthermore, in a structure that is arranged so as to detect, using position sensors, or the like, this location of the disk of the rim wheels through elastic linkage of a rim wheel to a disk part, as described in the aforementioned JP-A-2002-316502, the rigidity of the wheel itself is reduced by the necessity of the elastic linkage of the rim wheel to the disk part, which may have a negative impact on the stability of travel. Furthermore, since the sensor is located in a position that is extremely near to the tire, there is a problem in the ease with which the sensor may be damaged by gravel, mud, etc., thrown up from the road surface.
In consideration to the problems with the conventional structure like described above, the present assignees have already submitted U.S. patent application No. 10/795,152, proposing an anti-vibration device for a suspension that provides detecting assembly for detecting the load that acts between the vehicle body and the wheel. This type of anti-vibration structure for a suspension can be achieved through, for example, equipping a sensor for detecting loads or amounts of displacement relative to a suspension bushing, thereby enabling more accurate load detection than load detection based on tire deformation, or the like, doing so without a negative impact on the strength of the axle, the rigidity of the wheel, the performance of the tire, etc.
However, as the present assignees performed even more experimentation and research, it became clear that there was still room for improvement in the structure that use the invention from the prior application.
Specifically, when the wheels are attached to the vehicle body through the plurality of suspension bushings and detecting assembly are equipped on suspension bushings, the response at each suspension bushing to the component of force of the load applied to wheel is detected. Accordingly, in order to estimate, from the detected signal, the external forces that act on the wheel, it is necessary to calculate the total force, as the load that acts on the wheel, based on the component forces that are calculated by the signals that are detected from each of the suspension bushings. This requires a large number of detector positions, which is not only disadvantageous in terms of cost, but also problematic in terms of the difficulty of calculation.
Moreover, not only is the behavior of the tire complex, but the suspension parts undergo relatively large dislocations depending on the behavior of the tire to dislocate in the direction of the load that is applied to the suspension bushing. In some cases there are load inputs not only in the axial direction of the bushing and in a direction that is perpendicular to the axial direction of the bushing, but also input loads in a flexing direction and in the twisting direction, thus leading to the possibility of the occurrence of relatively large errors even in the calculation results that estimate the external forces that act on the wheels.
Moreover, the suspension bushing attachment angle, and by extension, the load input direction, also varies depending on the alignment (attachment angle) of the suspension parts. Therefore, when there are disruptions to the alignment of the suspension parts, due to impact loads on the wheels, there will also be deviations in the load detection of the suspension bushings, which can cause errors in the estimates of the external forces that act on the wheels.